1. Field of the Invention
The present invention relates to a knocking sensor for an internal combustion engine which is attached to the internal combustion engine and detects its knocking, and a manufacturing method of the same.
2. Description of the Related Art
As a knocking sensor for an internal combustion engine, a knocking sensor called a non-resonant type is disclosed in JP-A-2002-55013 (related art 1). This non-resonant type knocking sensor includes a base member having a cylindrical part and a flange part formed at its one end, a bolt is inserted into a center hole of the cylindrical part of the base member, and this bolt is attached to the internal combustion engine, so that the knocking of the internal combustion engine is detected.
In this kind of knocking sensor, an annular combination member including an annular piezoelectric element, an annular weight, a pair of annular terminal plates combined with these, and a pair of annular insulating sheets is disposed at the outer periphery of the cylindrical part, and this annular combination member is pressed to the flange part of the base member by a pressure fastening member. The annular weight gives moment of inertia based on the vibration generated in the internal combustion engine to the piezoelectric element. The piezoelectric element outputs an electric signal generated by the vibration according to the knocking of the internal combustion engine, and the electric signal is extracted from the terminal plates.
In the knocking sensor disclosed in the related art 1, electrogalvanizing is applied to the base member, and when whisker generated from the plating layer comes in contact with the pair of terminal plates, the terminal plates are electrically short-circuited, and there is a problem that the electric signal can not be extracted. Thus, a resin mold member is filled in an annular space between the annular combination member and the cylindrical part.
JP-A-2001-4476 (related art 2) also discloses a similar knocking sensor, and in the knocking sensor disclosed in the publication of JP-A-2001-4476, an insulating sleeve is disposed in an annular space between an annular combination body and a cylindrical part of a base member.
In the related art 1, since the resin mold member is filled in the annular space, four grooves are provided in the annular weight at intervals of 90 degrees. In order to generate sufficient moment of inertia, it is desirable that the weight of the annular weight is as large as possible. Thus, it is necessary to make the sectional areas of the four grooves as small as possible. However, when the sectional areas of the grooves are made small, passing areas of the resin mold filled through the grooves are lessened, so that it becomes difficult to send a sufficient amount of resin into the annular space.
In the related art 2, as the result of the addition of the insulating sleeve, not only the number of necessary parts is increased, but also the assembling operation of the insulating sleeve is also required to be performed, and therefore, the manufacture cost is increased.